The age of the Hinneryd granite ‐ its significance for interpreting the terranes of the southern Baltic Shield

Abstract

The adamellitic (monzogranitic) Hinneryd granite occurs in the southern region of the Eastern Segment, which is part of the Southwest Swedish Gneiss Complex. The granite is strongly foliated and pervasively metamorphosed. Near‐concordant zircon fractions (less than c. 15% discordant) define a U‐Pb upper‐intercept age of 1548+10 Ma interpreted as the intrusion age. E_ND(1548) is +0–5 and the depleted‐mantle Sm‐Nd model age is 1.84 Ga. Sm‐Nd isotope equilibrium is not established among the mineral phases. Two mineral isochrons are obtained by using different mineral‐whole‐rock combinations; these isochrons correspond to Sveconorwegian ages, 1065137 and 896±54 Ma (2a). The best‐fit line (1065 Ma) is obtained from phases that define the upper amphibolite‐facies assemblage and the foliation. The metamorphic mineral assemblage suggests temperatures of c. 650°C and pressures of c. 1 GPa. No contemporaneous granite is known from the northern region of the Eastern Segment. This supports earlier suggestions of a terrane boundary between the northern and southern regions of this Segment. The intrusion age of the Hinneryd granite is within errors identical to that of the West Glimåkra granite, also occurring in the Eastern Segment. The chemical compositions and depleted‐mantle ages indicate that their protoliths are different, suggesting a complex early history of the Segment. Chemical differences between the Hinneryd granite and contemporaneous granites in the Western Segment are apparent, but this is not taken to support any suggestion of a terrane boundary between the Western Segment and the southern region of the Eastern Segment.

Lindh, A., 1996: The age of the Hinneryd granite ‐ its significance for interpreting the terranes of the southern Baltic Shield. GFF, Vol. 118 (Pt. 3, September), pp. 163–168. Stockholm. ISSN 1103–5897.

Keywords:

• Zircon age
• depleted‐mantle model age
• Sm‐Nd mineral isochron
• geochemistry
• Proterozoic
• Baltic Shield
• Southwest Swedish Gneiss Complex
• Eastern Gneiss Segment
• Hinneryd granite
• Sweden